Selecting the correct rubber grade and mount for a particular engine or generator is a skilled task and your distributor will advise. For those who wish to study the science, the chart above shows how much deflection (or squash) will occur on each mount and each rubber hardness given a particular weight on the mount. In general you should aim for 3mm on the 50210, 4mm on the 50220, 5mm on the 50230 and 6mm on the 50240. The numbering system is simple: A 50223 mount is the 50220 model with number three rubber hardness and so on. Some engines, particularly those with less than four cylinders, require particular care and your distributor will help with these.